Linkage position dictates non-radical pathway selectivity on grafted biochar for peroxymonosulfate activation

Non-radical species, featuring mild oxidizing ability and high electrophilicity, exhibit great potential in sustainable water purification. However, their practical applicability is hindered by inherent competition of multiple reactive species and imprecise regulation of non-radical pathways on demand. Herein, we demonstrate that the linkage position of active site on catalyst matters in regulating the non-radical pathway of peroxymonosulfate-based advanced oxidation process (PMS-AOPs). The ortho- and para-linkage modified biochar catalysts (BIO-O-COOH and BIO-P-COOH) with thiocarbonyl sites were constructed by covalent-grafted linkage position engineering. Notably, the experimental and mechanistic studies indicate that stronger PMS adsorption on BIO-O-COOH, induced by the ortho effect of thiocarbonyl sites with amide groups, promotes PMS cleavage into *OOH intermediate for selective ¹O₂ generation, whereas moderate binding on BIO-P-COOH arising from para effect of the same moieties facilitates the formation of catalyst-PMS* complexes for the electron transfer pathway (ETP). Moreover, the capacity of BIO-O-COOH to efficiently utilize PMS for high-yield ¹O₂ production (422.7 μM) enables effective and selective pollutant degradation (k_obs = 0.177 min^-1), outperforming the BIO-P-COOH/PMS (k_obs = 0.042 min^-1) and most reported PMS-AOP systems. This work provides a facile strategy to design robust PMS activator for regulating targeted non-radical pathway, holding great prospects for broader applications.